1. Field of the Invention
The present invention relates to an electrode for an electric storage device, an electric storage device and a manufacturing method of an electrode for an electric storage device.
2. Description of the Background Art
A capacitor of electric storage devices is widely used in various electric equipments and the like. Among many types of capacitors, an electric double layer capacitor and a lithium-ion capacitor have a large capacity and particularly receive attention during recent years.
An electric double layer capacitor is an electric storage device including a cell, a hermetically sealed case for securing electrical insulation between cells and for preventing liquid leakage, a current collecting electrode for externally drawing electricity, and a lead wire. The cell principally includes a pair of opposed activated carbon electrodes, a separator for electrically isolating the electrodes from each other, and an organic electrolytic solution for developing a capacity.
Further, a lithium-ion capacitor is an electric storage device that uses an electrode capable of electrostatically adsorbing/desorbing ions, such as an activated carbon electrode, for a positive electrode, and uses an electrode capable of occluding lithium ions, such as hard carbon, for a negative electrode.
Energy stored in an electric double layer capacitor is expressed by the following equation (1):W=(½)CU2  (1)
wherein, W represents energy (capacity) stored, C represents a capacitance (depending on a surface area of an electrode), and U represents a cell voltage, respectively.
It is considered from the equation (1) that an improvement in capacitance contributes to an improvement in the energy to be stored.
In order to improve a capacitance in an electric double layer capacitor, Japanese Patent No. 3924273 (Japanese Patent Laying-Open No. 2005-079505) discloses “An electrode material of an electric double layer capacitor, which is made of a gel-like composition composed of an ionic liquid and a carbon nanotube obtained by applying shear force to the carbon nanotube in the presence of an ionic liquid for subdivision”.
Japanese Patent Laying-Open No. 2009-267340 discloses “An electrode for an electric double layer capacitor, wherein a sheet obtained by molding a carbon nanotube having a specific surface area of 600 to 2600 m2/g into a sheet is integrated with a base material constituting a current collector and having projections and depressions at the surface by the projections and depressions”.